This invention is generally directed to a novel system that determines whether the trailer door is open or closed. This information can be relayed to a trailer tracking system or to the semi-tractor so that this information can be used accordingly.
Some prior art systems sense the presence of a door using a mechanical limit switch. As the door closes, the arm of the mechanical limit switch is moved to indicate that the door is closed. This type of system is believed to have been used by Trucklite, a New York based automotive lighting and electronics company.
Other prior art systems use magnetic based switch technology to sense the status of the door. A magnetic target is mounted to the door and a reed switch is located on the sidewall where the door swings back to when fully opened. When the door is opened, the magnetic target comes into sensing range of the reed switch. The reed switch senses the magnetic target to indicate that the door is open. This type of system is believed to have been used by Vehicle Enhancement Systems (VES) and Vantage Tracking Solutions.
Another prior art system, used in 1996, used a magnet biased reed switch, mounted in the corner of the door frame that would sense the inside, steel skin of the door when the door was closed. Yet another prior art system, used in 1999, used a magnet biased reed switch in conjunction with a steel target plate to sense the position of the door. The reed switch was mounted to the door so that when the door was closed, the target plate would be in range of the reed switch and the door would be sensed as closed. These systems were developed and have been used by the assignee of the present invention.
In the prior systems in which a secondary component apart from the sensor is needed, more parts are provided which need to be inventoried and maintained. In addition, the sensor can be installed and working, but the secondary component (for example, the target plate or the magnet target) could be removed (either through accident or on purpose) and not replaced. If this occurs, because the secondary component is missing and in the situation where the door is closed, the prior art sensing system would sense that the door is open. In the prior art system in which the sensor was mounted in the corner of the door frame and sensed the inside, steel skin of the door when the door was closed, the sensor can be knocked off when materials are being loaded into the trailer.
The present invention provides a novel system for sensing whether a door of a trailer is open or is closed which uses a sensor and a standard component of the locking mechanism on the door of the trailer. The present invention does not require a secondary component to sense the door. This enables the system to be easier to install and easier to maintain than prior art systems. In addition, in the preferred embodiment of the system of the present invention, the status of the sensor can be monitored more readily than in the prior art systems. Because the secondary component is eliminated in the present invention, the situation where the door is closed, but the secondary component is missing so that the sensor senses that the door is open is eliminated. Other features and advantages of the present invention will become apparent upon a reading of the attached specification in combination with a study of the drawings.
A general object of the present invention is to provide a novel system for sensing whether a door of a trailer is open or is closed.
Another object of the present invention is to provide a novel system for sensing whether a door of a trailer is open or is closed by using a standard component of the locking mechanism of the trailer door.
Yet another object of the present invention is to provide a novel system in which the status of the sensor can be determined.
A further object of the present invention is to provide a novel system which is easy to install and maintain.
The present invention discloses a novel system for sensing whether a door of a trailer is open or is closed. A sensor is provided on the rear door frame proximate to the lockrod keeper of a conventional locking mechanism. The sensor senses the presence of the heel portion of the lockrod cam when the lockrod is engaged with the lockrod keeper. Control circuitry on the trailer processes and uses signals from the sensor to perform various functions.